Sprint Filter P08 F1-85 Air Filter for Racing – Royal Enfield Goan Classic 350 (2025–2026) CM231S F1-85

The word Racing in this title came from the filter, not from the motorcycle. Sprint Filter attaches it to the F1-85 medium wherever that medium appears in its catalogue, and the catalogue happens to list the CM231S F1-85 for the Goan Classic 350 airbox. Nothing in that arrangement says a Goan Classic is a race bike, and nothing about fitting the element makes it one. Reading a medium label as a description of the machine underneath it is the most common way to end up with the wrong filter, so the two are worth separating before anything else.

Key Features

• The racing medium from the Sprint Filter range: dry polyester, 85 µm, 15,000 l/m²/sec
• By Sprint Filter's own account the most used air filter in MotoGP, Moto3, World Superbike, Supersport and Superstock
• Retains 95.22 % of 100-micron particles in the manufacturer comparison
• No oil in service, so nothing can be over-applied and nothing can travel forward
• Roughly twice the filtering surface of other performance elements, in the series housing
• Direct replacement in the standard airbox with no remap; two years of warranty

What the paddock record does and does not transfer

The claim in the list above is the manufacturer's, not an independent measurement, and even taken at face value it describes engines that share very little with a 350 cc single. What travels from a grid to a road bike is the fabric and the way it is made. What does not travel is the context around it: sessions measured in minutes, engines stripped between them, and intake systems reworked to the point where the filter is genuinely part of the limit.

The Goan Classic case, plainly

This machine reaches its owner with a standard airbox, standard fuelling and a service interval counted in kilometres. Against that, the element asks a little over three times what the standard filter for the same box asks, and returns a coarser rating in exchange for flow the engine will never call on. It adds nothing to output either, because a drop-in filter does not make a standard 350 single noticeably stronger. The standard medium is the better purchase here by a wide margin.

Care and cleaning

The routine is dry and short: compressed air on the clean face, worked outwards through the weave, then straight back into the box. Anything oily that air leaves behind comes out with lukewarm water and a mild washing-up liquid, rinsed clear. Let it dry in open air and nowhere near heat or flame, then refit it untreated. The CM231S F1-85 maintenance sheet is in the Downloads tab.

Fitment & Compatibility

Catalogued for the Royal Enfield Goan Classic 350 in 2025 and 2026. The same element serves five bikes in this family: besides this one, the Bullet 350, the Classic 350, the Hunter 350 and the Meteor 350. Model years are set out under Fitment.